12.1.3—NOx sources and catalytic removal
- Syllabus
- 9701–2028–2029
- Objective
- 12.1.3
- Level
- AS
Catalytic converters reduce NOx by converting harmful gases into less harmful products
Nitrogen oxides form naturally in high-temperature combustion and are also produced by human activities. In a catalytic converter, NOx is reduced while carbon monoxide and hydrocarbons are oxidised.
A simplified reaction is 2CO + 2NO → 2CO₂ + N₂. The catalyst provides a lower-energy pathway; it does not remove the underlying production of pollutants or make every exhaust gas harmless.
A three-way converter uses a precious-metal surface so CO can reduce NO to N₂ while CO becomes CO₂. Oxygen availability and engine conditions affect which reactions dominate.
Do not say the catalyst “destroys” nitrogen or shifts an equilibrium. It changes reaction rate and the products depend on the exhaust composition.
ConceptA-Level CAIE Chemistry AS